A large number of variable valve timing mechanisms have been proposed in the prior art for use in internal combustion engines and certain of such engines presently being manufactured have been equipped with mechanisms of this type. Some of the variable valve timing mechanisms that I have proposed for use in internal combustion engines are disclosed in the following U.S. patents and patent applications:
U.S. Pat. No. 5,673,659 entitled "LEAD SCREW DRIVEN SHAFT PHASE CONTROL MECHANISM", issued on Oct. 7, 1997. PA1 U.S. Pat. No. 5,860,328 entitled "SHAFT PHASE CONTROL MECHANISM WITH AN AXIALLY SHIFTABLE SPLINED MEMBER", issued on Jan. 19, 1999. PA1 U.S. patent application Ser. No. 09/283,019, entitled "TWO PART VARIABLE VALVE TIMING DEVICE", filed on Apr. 1, 1999. PA1 U.S. patent application Ser. No. 09/384,680 entitled "PHASE CHANGING DEVICE" filed on Aug. 27, 1999. PA1 U.S. patent application Ser. No. 09/384,804 entitled "CAMSHAFT PHASE CONTROLLING DEVICE" filed on Aug. 27, 1999.
One characteristic of each of the mechanisms disclosed in the above-mentioned patents and patent applications is that they are all intended to be custom-made for the engines, i.e., integrally designed as part of the cylinder head and valve train mechanism of the engine. This approach can be expensive because the mechanism normally does not lend itself well for use across-the-board on different engines. In other words, there is no total unit interchangeability and, therefore, no cost reduction based on very large production volumes. This is true especially in cases where the mechanism is only being used on low volume top-of-the-line car models. The cost can also be increased if the mechanism is incorporated into the cylinder head and the valve train as the cylinder head is assembled on the engine. As new internal combustion engines are designed with variable valve timing devices, it is important to produce identical low-cost variable valve timing mechanisms suitable for uses on a variety of engines. With the possibility of large volumes, it would be possible to lower costs by designing better variable valve timing mechanisms with improved materials and higher durability.
Each of my patent applications identified above as items 3-5, disclose variable valve timing mechanisms that utilize a novel method of replacing splines by low-friction, low-wear encapsulated ball splines to angularly index the camshaft in relation to the camshaft drive gear. Another difference in these mechanisms, as compared to the prior art hydraulically operated mechanisms, is that the operational force is provided both ways by electrically driven stepper motors. In addition, the above patent applications also disclose a novel method of axially moving a shifting sleeve by using a low friction encapsulated ball lead screw as a linear motion device.